Became brighter or more luminous; made something lighter or more cheerful; improved in mood or outlook.
From Old English 'beorht' (bright) combined with the suffix '-en' to form a verb, plus '-ed' for past tense. The word has been used in English for over a thousand years with consistent meaning.
When researchers studied what makes people happy, they found that literal brightness matters more than we think—bright rooms and sunny days actually change brain chemistry and mood, so 'brightened' is both metaphorical and biological.
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